Enteroviruses

Enteroviruses (EVs), so named because most members infect the alimentary tract and are shed in the feces, cause a variety of diseases in humans and lower animals. They constitute one of the six major subgroups, or genera, of the family Picornaviridae [ pico , “small”; rna , “ribonucleic acid”]. The other genera of Picornaviridae are the Rhinovirus , Cardiovirus , Aphthovirus , and two newly designated genera, Hepatovirus , the prototypic member of which is human hepatitis A virus; and Parechovirus , which contains two serotypes that were previously classified as echoviruses types 22 and 23, and at least 14 additional serotypes. Physical and biochemical properties EVs, like all members of the picornavirus family, are small, nonenveloped, spherical (icosahedral) viruses approximately 30 nm in diameter. Their capsids consist of 60 structural subunits, each composed of 4 unique polypeptides: VP1, VP2, VP3, and VP4. Their genome consists of a linear, single-stranded, unsegmented molecule of RNA (of approximately 7500 nucleotides) that has the same polarity as messenger RNA. EVs are stable over a wide range of pH (pH 3 to 10), permitting them to retain infectivity during passage through the gastrointestinal tract. They are not inactivated by ether, alcohol, or other lipid solvents, but are readily inactivated by formaldehyde or phenol. EVs retain infectivity for days at room temperature, weeks at refrigerator temperature, and indefinitely when frozen at −20°C or lower. Molar MgCl 2 further increases their thermostability, facilitating the use of oral polio vaccines in tropical areas where availability of refrigeration is limited.